The present invention concerns a leakage detection system for tanks used to store electrically conductive fluids. The invention was developed specifically for detecting leaks from large tanks storing radioactive wastes.
Proper radioactive waste management is becoming increasingly important as the use of nuclear energy for generation of electric power increases. Conventional nuclear power plants produce a considerable amount of radioactive waste material, which in turn must be stored in a manner so as to prevent harm to human beings and/or contamination of the environment.
Although radioactive wastes are currently being disposed of in a variety of ways, one of the most common methods involves neutralizing the acidic nitrated radioactive waste material with an alkali, producing a salt solution, which is then stored in large, specially designed and constructed, tanks which may either be buried underground or stored in underground facilities.
Even though such storage tanks have been specially designed to contain, long-term, the radioactive waste solution, it has been found, particularly over the past several years, that a significant percentage of the original storage tanks have developed leaks, due to the effect over time of the extremely corrosive waste solution. With respect to the storage tanks already in use, as well as those which are currently being designed and manufactured, it is extremely important that any leakage of the waste solution be minimized.
Furthermore, if and when leaks do develop in such storage tanks, it is vital that they be quickly and accurately detected. By early detection, damage to the storage environment (i.e. the surrounding soil) can hopefully be minimized, and the basic integrity of the storage tanks maintained over a considerable period of time.
Presently, however, existing instrumentation for the detection of leaks, which typically take the form of a float for sensing liquid level in a tank, have a minimum resolution capability of approximately 8,000 gallons. In addition, frequent pumping of waste into and out of storage tanks equipped with float sensors causes level changes which mask a slow loss of waste solution. Substantial damage both to the storage environment and the tank itself can thus occur before a leak can be detected by existing detection systems.
Furthermore, such conventional leak detection systems must be used within the tank itself. The harsh environment within the tank inevitabily leads to a degradation of performance of the leak detection system, thereby creating additional problems of system monitoring and replacement.
In view of the above, it is a general object of the present invention to provide a leak detection system for storage tanks containing electrically conductive fluids, specifically, underground radioactive waste storage tanks, which overcomes one or more disadvantages of the prior art specified above.
It is another object of the present invention to provide such a detection system which may be located external to the tank under test.
It is a further object of the present invention to provide such a detection system which has the capability of detecting leaks within a short time after they occur.
It is an additional object of the present invention to provide such a detection system which is capable of detecting a leak of less than 50 gallons.
It is yet another object of the present invention to provide such a detection system which is capable of accurately locating the place of the leak on the tank.
It is a still further object of the present invention to provide such a detection system which is useful within a tank farm.
It is an additional object of the present invention to provide such a detection system which may be selectively actuated to measure each tank in turn in a tank array.
It is a still further object of the present invention to provide such a detection system which operates under widely varying nominal soil conditions and is insensitive to normal weather variations.
It is a still further object of the present invention to provide such a detection system which detects leakage of electrically conductive fluid from any configuration of storage tank and/or its transfer pipes, into the storage environment, i.e., the soil surrounding the tank and/or transfer pipes.